Get Robot App Lock Status

Return the current state of the robot's managed-app lock.

The daemon's single source of truth for which managed app (if any) currently holds the robot:

• free: no managed app holds the slot.
• local_app: a Python app launched via AppManager is running. holder_name is the app name.
• remote_session: a remote WebRTC client is connected via the central signaling relay. holder_name is a generic "remote" placeholder (the real consumer app name lives on the central server and is surfaced via its own /api/robot-status).

Note that SDK clients talking to the daemon directly bypass this lock; it only reflects the two managed app entry points.

Intended for UI layers (desktop app, dashboard) that want to render a busy/free indicator without trying to open a session.